class PythonClass:
    instance_num = 0

    @classmethod
    def check_cls_nums(cls):
        print(cls.instance_num)

    @classmethod
    def modify_cls_nums(cls, num):
        cls.instance_num = num

    def __init__(self):
        PythonClass.instance_num += 1


if __name__ == '__main__':
    ins1 = PythonClass()
    ins2 = PythonClass()
    print(PythonClass.instance_num)
    ins3 = PythonClass()
    print(ins3.instance_num)
    ins1.modify_cls_nums(99)
    ins4 = PythonClass()
    print(ins1.instance_num)
